Fluid working machines, such as pumps, motors and machines which are operable as a pump or a motor in alternative operating modes, include low and high pressure fluid lines and working chambers of cyclically varying volume (such as piston cylinders). Pumps receive working fluid from the low pressure fluid line, do work to pressurise it and deliver it to the high pressure fluid line; motors receive pressurised working fluid from the high pressure line, use it to do work, and deliver the depressurised fluid to the low pressure line. Valves employed to regulate the flow of working fluid between the low and high pressure fluid lines and the working chamber are referred to herein as low and high pressure valve respectively.
The invention concerns actuated valves, in which an actuator urges the low and high pressure valves to open or close as appropriate. Such valves are useful for fluid working machines such as those disclosed in EP0361927 and EP0494236, which are machines in which electronically controlled valves are actively controlled in phased relation to cycles of working chamber volume by a controller to determine the net displacement of working fluid by each working chamber during each cycle of working chamber volume.
WO2013018146 A1 (Mitsubishi Heavy Industries, Ltd.) discloses a pair of valve members influenced by a single solenoid coil. The invention of the present application also employs a single actuator to influence a pair of valve members, however the inventive aspect is the physical arrangement of internal components leading to a more compact valve.
Machines of this type are useful in applications such as industrial, automotive, renewable power generation or vehicles, where it is important that the machines be compact and low cost. It is advantageous to provide a valve unit comprising both the low and high pressure valves.
It is also advantageous to provide a valve unit in which the low and high pressure valves are both actuated by the same actuator (e.g. a single solenoid). This is advantageous because it reduces the complexity of the valve unit, and its size, and can increase reliability. By positioning the armatures closer to the solenoid than in previous designs, the present invention reduces the length of magnetic paths, hence reducing losses and increasing efficiency.
The invention concerns improvements to the structure of such a valve unit, which have advantages including one or more of simplifying manufacture, increasing reliability, making the valve unit more compact for a given flow capacity, reducing the total dead space of the resulting machine (i.e. the volume of working fluid between the working chamber and the valves, when both valves are closed and when the working chamber is at its minimum volume), and reducing magnetic losses (and therefore improving energy efficiency).